This paper proposes a solution to contrast agent (CA) detection in angiograms by considering x-ray images as intensity images and applying mathematical morphology operators. We present two detection approaches, one based on the intensity infimum and the other based on the dual reconstruction. The evaluation using several data sets shows that both techniques are able to detect the presence of the contrast medium volume. Moreover, the dual reconstruction–based method is proven to be faster in processing time and more effective than the intensity infimum–based method in distinguishing the intensity change at the same location from the displacement of the same region. In addition, we show how to track the CA passage through a region of interest by observing the intensity evolution in successive submasks.